Cassowaries (genus Casuarius) are very large flightless birds native to the tropical forests of New Guinea and northeastern Australia.

The Southern Cassowary is the third largest flightless bird on the planet, smaller only than the ostrich and emu. Cassowaries feed mainly on fruits, though all species are truly omnivorous and will take a range of other plant food including shoots, grass seeds and fungi in addition to invertebrates and small vertebrates.

Cassowaries are very shy, but when disturbed, they are capable of inflicting fatal injuries to an adult human.

A cassowary's three-toed feet have sharp claws; the dagger-like middle claw is 120 mm (5 inches) long. This claw is particularly dangerous since the Cassowary can use it to kill an enemy, disembowelling it with a single kick.

Cassowaries can run up to 45-50 km/h (32 mph) through the dense forest. They can jump up to 1.5 m (5 feet) and they are good swimmers.

Cassowaries have horn-like crests called casques on their heads. These consist of "a keratinous skin over a core of firm, cellular foam-like material". The casque has several purposes. Cassowaries put their heads down and used to part vegetation and move through dense rainforest. They use it as a weapon for dominance disputes, as well as the casque amplifies deep sounds and is beleived to be used for either sound reception or acoustic communication.

The birds also lower their heads when they are running "full tilt through the vegetation, brushing saplings aside and occasionally careering into small trees. The casque also helps protect the skull from such collisions.

Diet
Cassowaries are frugivorous; fallen fruit, such as the cassowary plum and fruit on low branches is the mainstay of their diet. They also eat fungi, snails, insects, frogs, and snakes. They are a keystone species of rain forests because they eat fallen fruit whole and distribute seeds across the jungle floor via excrement.

Role in seed dispersal and germination
Casuarius casuarius scat

Cassowaries feed on the fruits of several hundred rainforest species and usually pass viable seeds in large dense scats. They are known to disperse seeds over distances greater than a kilometre, and thus probably play an important role in the ecosystem. Germination rates for seeds of the rare Australian rainforest tree Ryparosa were found to be much higher after passing through a cassowary's gut (92% versus 4%).